includes cache of latest version and page to view if updates are
available with a link to the latest update's release notes and a link to
check for the latest update now, refreshing the cache manually.

This upgrades the library to v2, which lets you specify that GOMAXPROCs
should always be the max number of CPUs -- and then sets it to that.

One side effect of this is that images are no longer listed in sitemaps.
I'm somehow at a loss on how to build and append the images array we
need, with the library's latest changes.

Fixes #86

This adds https://github.com/jteeuwen/go-bindata as a module dependency
as the make target 'build' will result in it's addition.

This indicates whether or not invites are enabled on this instance. It
requires an upgrade to writefreely/go-nodeinfo v1.2.0